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There are two loci that influence coat colour in horses. The first locus black (B) is...

There are two loci that influence coat colour in horses. The first locus black (B) is dominant to chestnut (b). The second locus possesses a gene that masks all others and is referred to as dominant white (W). Dominant white is lethal during gestation when homozygous. When found in a homozgygus recessive form (ww) colour from the B loci is expressed. What would be the genotypic and phenotypic ratios for the following matings

a. BBww × BbWw

b. Bbww x bbww

c. BbWw x bbWw

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Answer #1

Soulution:

First locus- The black 'B' dominant to chetnut 'b'. BB and Bb produces Black coat , bb produces chestnut coat.

Second locus- White 'W' dominant to all other alleles. If 'W' presents no other colour express, and all phenotypes will be white. Only in  'ww' homozygous recessive condition B loci (first locus) is expressed

a.BBww x BbWw

Bw Bw Bw Bw
BW BBWw BBWw BBWw BBWw
Bw BBww BBww BBww BBww
bW BbWw BbWw BbWw BbWw
bw Bbww Bbww Bbww Bbww

Genotype ratio

BBWw : BBww : BbWw ; Bbww = 3 : 3 : 3 ; 3 i.e 1: 1 : 1 : 1

Phenotype ratio

BBWw - White

BBww - Black

BbWw - White

Bbww - Black

White : Black = 6 : 6 i.e 1 : 1

b. Bbww x bbww

Bw Bw bw bw
bw Bbww Bbww bbww bbww
bw Bbww Bbww bbww bbww
bw Bbww Bbww bbww bbww
bw Bbww Bbww bbww bbww

Genotype ratio

Bbww : bbww = 8 : 8 i.e 1:1

Phenotype ratio

Bbww - Black

bbww- Chesnut

Blck : Chesnut = 8 : 8 i.e 1 : 1

c. BbWw x bbWw

BW Bw bW bw
bW BbWW BbWw bbWW bbWw
bW BbWW BbWw bbWW bbWw
bw BbWw Bbww bbWw bbww
bw BbWw Bbww bbWw bbww

Genotype ratio

BbWW : BbWw : Bbww : bbWW : bbWw : bbww = 2 : 4 : 2 : 2 : 4 :2 i.e 1 : 2 : 1 : 1 : 2 : 1

Phenotype ratio

BbWW - White

BbWw - White

bbWW - White

Bbww - Black

bbWw - white

bbww - Chestnut

White : Black : Chestnut = 12 : 2 : 2 i.e 6 : 1 : 1

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